A bogie of a railcar has been an important device that influences a running performance and ride quality of the railcar. As a basic function and performance, the bogie has an important role of smoothly travelling on the tracks while supporting a carbody, on which passengers, cargos, and the like are loaded, from under the carbody.
Therefore, the bogie is constituted by: an electric motor as a drive mechanism; brakes; wheels; axles; bolster springs (air springs) for running stability; axle springs; and a bogie frame that supports these components.
Nowadays, a “bolsterless bogie” not including a bolster beam (bolster) provided between the carbody and the bogie frame has been developed from a conventional “bolster beam type bogie” including the bolster beam (bolster) provided between the carbody and the bogie frame, and in particular, an “axle arm type bogie” is becoming mainstream (see PTL 1 (Japanese Laid-Open Patent Application Publication No. 9-301163), for example).
The axle arm type bogie receives the entire load of the railcar in order of a cross beam of the carbody, a bolster beam, a bolster spring (air spring), a bogie frame, an axle spring, an axle box, an axle, a wheel, and a rail. FIG. 12 is a partial enlarged to view schematically showing this axle arm type bogie, and FIG. 13 is an arrow view when viewed from a direction A of FIG. 12.
A bogie 100 includes: a pair of side sills 102 and 104 arranged parallel to the rail; and a pair of cross beams 106 and 108 arranged between the side sills 102 and 104 so as to be parallel to a sleeper of the rail.
Axles 110 and wheels 112 are arranged between the side sills 102 and 104 so as to be rotatably attached to the side sills 102 and 104 via axle boxes 114. To transfer a pulling force and a brake force between the bogie 100 and each of the axle boxes 114, each of axle box suspensions 120 rotatably attached by shall portions 118 is interposed between the side sill 102 or 104 and the axle box 114 so as to be movable in an upper-lower direction in accordance with an operation of each of coil-shaped axle springs 116. Fifty percent of the entire weight of the railcar is the weight of the bogie, and the bogie is constituted by a steel structure large frame and steel springs.